Due to the nature of the PacRim event a lot of people are discovering the realm of Mach numbers for the first time. Others have been there but trusted the simple view that there are 'dependable' numbers that can be used to measure Mach and related performance.
First, here's a link to a specific reply I made to a query about a Duenna.
http://www.sim-outhouse.com/sohforum...l=1#post402137
There has also been a lot of discussion about "subsonic/supersonic" aircraft. It was allowed in the PacRim that an aircraft would be deemed OK if it could be tested and flown and unable to exceed Mach 1.00 in level flight.
Assuming that everyone complied with 'standard' test procedures for this - Wx set to "Clear skies", aircraft tested at multiple altitudes from Sea Level to near service ceiling, - we have done the tests on pilot's honour and allowed numerous aircraft that have not complied with the "old rule" of a .cfg file with a listed Mmo of "less than M 1.00 We have demonstrated reliably the principle that the Mmo (Max. Operating Mach Number) is just that.. an aerodynamic MAXIMUM, not what the aircraft can maintain in level flight. (ie. ' It won't go that fast unless you dive it and then prepare to get hurt if you exceed the Mmo'). Now, the next question is whether we trust each other to do the testing properly. I'm beginning to wonder if we do... but that is a different can of worms.
However, it must be remembered that "Mach" is a variable. The empirical test shows the speed of sound (Mach 1.0) is 661 Kts at Sea Level in International Standard Atmosphere (ISA = 29.92"Hg and 15*Celsius) or roughly equivalent to MSFS "Clear Skies"). The link I posted in the above thread is repeated here:
http://www.militaryfactory.com/aircraft/mach.asp
and I am sure you can find many more references and tables.
What is critical for us is that we don't fly in ISA - we use Real World Weather. Temperature varies, pressure varies, winds vary. No single Duenna data point will conclusively show what is happening. Duenna produces:
- A max GS -but GS is dependent on winds vs airspeed - so it does not show pure AIRSPEED and only indicative of speed over the ground - not though the air.
- A Max IAS - but that is a) transient moment-by-moment; b)affected by temp. , pressure, rate of climb/descent so it is not a measure of level flight speed either
- Duenna does not show atmospheric data at each reporting point so there is no way to know what the IAS/Mach relationship is at any given moment.
Certainly, an acceptable (M 0.99 or less in level flight) aircraft might well exceed Mach 1 in a dive (which is allowed) but consider the mechanics of it... Most aircraft I have tested require a significant dive (in excess of 5000 ft/min) to exceed M 1.0 so even a dive from 35000 ft will not be of much advantage and besides, the Race speed is NOT calculated from a Mach number or IAS but from Distance /Time so a few minutes of 700 Kts IAS are not going to have an impact over a race of 20+ hours! Additionally, ALL of you can test the limits of the aircraft if you are willing to take the chance on any leg.
As for the "apparent excessive speeds" you may see in a Duenna snapshot, look at these screenshots (remembering that old bit about 661 Kts at Sea Level)
1. Test flight at Darwin descending from 5000 Ft in "Clear Wx" note the Mach # and IAS
2. Same test in Real World weather at Darwin...
3. AFSD showing atmospheric data moments after the previous picture - note temp and pressure values -NOT ISA to be sure!
4. In an effort to put this together quickly, the test pilots pushed the envelope. Photo shows nose gear damage from a "too high" extension speed on approach. Repair bills are being sent to the PacRim participants.
In summary, the whole issue of "transonic" flight is a lot more complex that a few numbers in a snapshot view - just ask the guys who supported aircraft like the X-1. No simple rule and no simple look at the MSFS flight envelope is going to give a perfect answer. For all practical purposes, and over the long term, as long as an aircraft can be shown to be incapable of reaching/maintaining/exceeding Mach 1.00 IN LEVEL FLIGHT IN ISA conditions, it should be good enough.
As for the odd, temporary anomaly, perhaps we should look at rules that require a 24-72 hour maintenance period (even better, a slow-speed ferry flight to a maintenance base) for any reported overspeed or exceeding a "G" limit in flight or on landing (real-world commercial aircraft have sensors in the gear to show the latter and it requires logbook entries and an inspection). Ya Think????
The Committee in this event wanted simplicity to satisfy a request from pilots. The mystery is then why pilots want to nitpick the application of those rules - which can only result in tougher, tighter, more complex rules to "fix" the perceived unfairness or misuse.
MaddogK
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